Total Internal Reflection Microscopy (FZJ - ICS3)
Light Scattering
Description
DESCRIPTION OF THE FACILITY
If a laser beam is totally internal reflected from a planar interface, the electric field penetrates the external phase, creating a so called evanescent wave, i. e. a wave propagating parallel to the interface with a field strength, which decays exponentially along the interface normal. The typical decay length at a glass/water interface is of the order of half the wavelength. The intensity that is scattered by a single colloidal particle located in the evanescent field monotonically decreases with the distance of the particle from the glass wall. Brownian motion of the particle normal to the interface causes intensity fluctuations, where the probability density to observe a certain value of scattered intensity is equal to the probability density of finding the particle at a certain separation distance. Thus the histogram of scattered intensities can be converted to the probability distribution of separations. The latter is used to calculate the particle/wall interaction potential from Boltzmann’s law.
DETAILS OF THE INSTRUMENTAL SET UP
DETECTION
single photon counting head, (Hamamatsu)CCD camera (Photometrics)
AVAILABLE ILLUMINATION WAVELENGTHS
440 and 632.8 nm
LASER POWER
50 mW at 440 nm
15 mW at 632.8 nm
PENETRATION DEPTH
100 nm <λ<200 nm
FORCE RANGE
50 fN < F< 0.1 pN
FORCE RESOLUTION
<10 fN
ENERGY RESOLUTION
approx. 1 kBT
OPTICAL TWEEZERS
optional
AVAILABLE SAMPLE ENVIRONMENT
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LOCATION
Facility available at Forschungszentrum Jülich, Germany, ICS-3
Instrument responsible
Yi Liu and/or Peter Lang
Local Contacts
- Dr. Yi Liu
- Prof. Peter Lang
